In recent years, liquid crystal display devices are widely used as display devices for monitors, projectors, mobile information terminals, mobile phones, and the like. Generally speaking, a liquid crystal display device allows the transmittance (or reflectance) of a liquid crystal display panel to vary with a driving signal, thus modulating the intensity of light from a light source for irradiating the liquid crystal display panel, whereby images and text characters are displayed. Liquid crystal display devices include direct-viewing type display devices in which images or the like that are displayed on the liquid crystal display panel are directly viewed, projection-type display devices (projectors) in which images or the like that are displayed on the display panel are projected onto a screen through a projection lens in an enlarged size, and so on.
By applying a driving voltage which corresponds to an image signal to each of the pixels that are in a regular matrix arrangement, a liquid crystal display device causes a change in the optical characteristics of a liquid crystal layer in each pixel, and regulates the transmitted light in accordance with the optical characteristics of the liquid crystal layer with polarizers (which typically are polarizing plates) being disposed at the front and rear thereof, thereby displaying images, text characters, and the like. In the case of a direct-viewing type liquid crystal display device, these polarizing plates are usually directly attached to a light-entering substrate (the rear substrate) and a light-outgoing substrate (the front substrate or viewer-side substrate) of the liquid crystal display panel.
Methods for applying an independent driving voltage for each pixel include a passive matrix type and an active matrix type. Among these, on a liquid crystal display panel of the active matrix type, switching elements and wiring lines for supplying driving voltages to the pixel electrodes need to be provided. As switching elements, non-linear 2-terminal devices such as MIM (metal-insulator-metal) devices and 3-terminal devices such as TFT (thin film transistor) devices are in use.
On the other hand, in a liquid crystal display device of the active matrix type, when strong light enters a switching element (in particular a TFT) which is provided on the display panel, its element resistance in an OFF state is decreased, thereby allowing the electric charge which was charged to the pixel capacitor under an applied voltage to be discharged, such that a predetermined displaying state cannot be obtained. Thus, there is a problem of light leakage even in a black state, thus resulting in a decreased contrast ratio.
Therefore, in a liquid crystal display panel of the active matrix type, in order to prevent light from entering the TETs (in particular channel regions), a light shielding layer (called a black matrix) is provided on a TFT substrate on which the TFTs and the pixel electrodes are provided, or on a counter substrate that opposes the TFT substrate via the liquid crystal layer, for example.
Now, in the case where the liquid crystal display device is a reflection-type liquid crystal display device, decrease in the effective pixel area can be prevented by utilizing reflection electrodes as a light shielding layer. However, in a liquid crystal display device which performs displaying by utilizing transmitted light, providing a light shielding layer in addition to the TETs, gate bus lines, and source bus lines, which do not transmit light, will allow the effective pixel area to be decreased, thus resulting in a decrease in the ratio of the effective pixel area to the total area of the displaying region, i.e., the aperture ratio.
Liquid crystal display devices are characterized by their light weight, thinness, and low power consumption, and therefore are widely used as display devices of mobile devices such as mobile phones and mobile information terminals. With a view to increasing the amount of displayed information, improving the image quality, and so on, there are stronger and stronger desires for display devices to have higher resolutions. Conventionally, it has been a standard to adopt QVGA displaying by 240×320 pixels for liquid crystal display devices of the 2 to 3-inch class, for example, but devices which perform VGA displaying by 480×640 pixels have also been produced in the recent years.
As liquid crystal display panels become higher in resolution and smaller in size, the aforementioned decrease in their aperture ratio presents a greater problem. The reason is that, even if there is a desire to reduce the pixel pitch, constraints such as electrical performance and fabrication techniques make it impossible for the TFTs, the bus lines, etc., to become smaller than certain sizes. It might be possible to enhance the brightness of the backlight in order to compensate for the decreased transmittance, but this will induce an increased power consumption, thus presenting a particular problem to mobile devices.
In recent years, as display devices of mobile devices, transflective-type liquid crystal display devices which perform displaying by utilizing light from a backlight under dark lighting and perform displaying by reflecting light entering the display surface of the liquid crystal display panel under bright lighting have become prevalent. In a transflective-type liquid crystal display device, a region (reflection region) which performs displaying in the reflection mode and a region (transmission region) which performs displaying in the transmission mode are included in each pixel. Therefore, reducing the pixel pitch significantly will lower the ratio of the area of transmission region to the total area of the displaying region (aperture ratio of the transmission region). Thus, although transflective-type liquid crystal display devices have the advantage of realizing displaying with a high contrast ratio irrespective of the ambient brightness, they have a problem in that their brightness is lowered as the aperture ratio of the transmission region becomes smaller.
As a method for improving the efficiency of light utility of such a liquid crystal display device including transmission regions, Patent Document 1 and Patent Document 2 disclose a method of providing microlenses for converging light in each pixel on the liquid crystal display panel in order to improve the effective aperture ratio of the liquid crystal display panel. Furthermore, the applicant discloses in Patent Document 3 a production method for a liquid crystal display panel with a microlens array, which is suitably used for transmission-type or transflective-type liquid crystal display devices and the like. According to the production method described in Patent Document 3, microlenses can be formed corresponding to the pixels in a self-aligning manner, with a high positional precision.
Generally speaking, a VA-type (vertical-alignment type) liquid crystal display device has high viewing angle characteristics as compared to those of a TN-type liquid crystal display device or the like, and using an optical film (polarizing plate+optical compensation element) on both sides of a VA-type liquid crystal display panel makes it possible to achieve displaying with a wide viewing angle and a high contrast. Herein, it is commonplace to employ the same optical film on the light-incident side and on the outgoing side, whereby a high optical compensation effect can be obtained.
As an example of a VA-type liquid crystal display device, Patent Document 4 describes a liquid crystal display device having a wide-viewing-angle polarizing plate on both sides of a liquid crystal layer, wide-viewing-angle polarizing plate being composed by attaching two different phase difference layers on a polarization film. Moreover, Patent Document 5 describes an example of a liquid crystal display device having microlenses. In there, in order to prevent a deterioration in contrast due to the provision of microlenses, a polarizer is disposed between the microlenses and a liquid crystal panel, rather than outside the microlenses.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2003-337207
[Patent Document 2] Japanese Laid-Open Patent Publication No. 2005-275142
[Patent Document 3] Japanese Laid-Open Patent Publication No. 2005-196139 (Japanese Patent No. 3708112)
[Patent Document 4] Japanese Laid-Open Patent Publication No. 2003-121642
[Patent Document 5] Japanese Laid-Open Patent Publication No. 5-188364